High Energy Shock Waves Activate 5 0 -Aminolevulinic Acid and Increase Permeability to Paclitaxel: Antitumor Effects of a New Combined Treatment on Anaplastic Thyroid Cancer Cells M. G. Catalano, 1 L. Costantino, 1 N. Fortunati, 2 O. Bosco, 1 M. Pugliese, 2 G. Boccuzzi, 1 L. Berta, 1 and R. Frairia 1 Objective: Multimodal treatments do not meaningfully improve survival of anaplastic thyroid cancer. Conse- quently, new effective therapeutic modalities are needed. The use of paclitaxel is under clinical investigation; it shows about a 50% response rate, but it is not able to alter the fatal outcome for patients with anaplastic car- cinoma. High energy shock waves (HESW) have been shown to cause a transient increase in the permeability of cell membranes thus allowing higher intracellular drug concentrations. 5-Aminolevulinic acid (ALA) is used in the photodynamic therapy (PDT) of cancer, and HESW are under evaluation for their use as an activator in ALA- PDT. Design: We investigated the effect of HESW produced by a piezoelectric generator on the sensitivity to paclitaxel and ALA treatments of two different anaplastic thyroid cancer cell lines (ARO and CAL-62). Cells, treated sequentially with ALA and paclitaxel were exposed to HESW; thereafter, cell viability and apoptosis induction were evaluated. Main outcome: Combined exposure to ALA, paclitaxel, and shock waves resulted in a significant enhancement of cytotoxicity and induction of apoptosis in thyroid cancer cells with respect to cells treated with paclitaxel alone. Conclusions: These preliminary data suggest the possibility of using HESW and ALA in combination with paclitaxel as a promising new therapy in the treatment of anaplastic thyroid cancer. Introduction T hyroid carcinoma is the most frequent malignancy of the endocrine system (1). About 90% of all cases are well-differentiated carcinomas that are successfully treated with thyroidectomy and radioiodine. However, over time, up to 30% of these tumors dedifferentiate and when the stage of anaplastic thyroid cancer (ATC) is attained, the tumor follows an aggressive course (2) and the prognosis becomes very poor (3). In addition, about 1% of thyroid cancers arise as undifferentiated tumors. Dedifferentiated tumors as well as those undifferentiated from the beginning are character- ized by resistance to conventional therapy and are almost always fatal within a few months from diagnosis (4). Fur- thermore, the use of chemotherapy and external-beam ra- diotherapy has been quite disappointing. Currently the most commonly used chemotherapic agent for ATC is doxorubicin with response rates of only approximately 22% (5). Com- bined therapy with cisplatin seems to increase response rate but it is associated with relatively high toxicity in most el- derly patients (6,7).As far as treatment with paclitaxel is concerned, a response rate of about 50% was obtained in a recent phase II clinical trial, but the treatment was unable to modify overall survival in patients with anaplastic thyroid cancer (8). The use of paclitaxel thus looks promising, but new treatment approaches are still required to improve the clinical course of the disease. High energy shock waves (HESW) were described as al- tering the growth characteristics of tumor cells in vitro and in vivo (9–13). Different tumor cell lines of human and animal origin were studied in order to get deeper into the mecha- nisms of interactions of ultrasound shock waves and tumor growth (14–18). Moreover, a significant enhancement of the cytocidal effect of some anticancer agents on tumor cell sus- pensions was obtained by the combination with shock waves (19–25). Another attractive and promising form of treatment for solid tumors is photodynamic therapy (PDT). It involves the administration of a tumor-localizing photosensitizer or pho- tosensitizer prodrug such as 5-aminolevulinic acid (ALA), a precursor in the heme biosynthetic pathway, and the sub- sequent activation of the photosensitizer by light (26). However, the low penetration depth of light through the skin and tissues limits the use of ALA-PDT to the treatment of su- perficial and endoscopically reachable tumors. To overcome this drawback, the sonodynamic therapy based on the ability 1 Department of Clinical Pathophysiology, University of Turin, Italy. 2 Oncological Endocrinology, ASO San Giovanni Battista, Turin, Italy. 91 THYROID Volume 17, Number 2, 2007 ª Mary Ann Liebert, Inc. DOI: 10.1089=thy.2006.0142